In conventional construction, a plumb line or bubble level is used for vertical surveying. However, a plumb may swing and it will be still in calm air for which a certain period of waiting has to elapsed. And it will be accurate only in such a situation. A bubble level is not precise enough and it can only be used as a rough reference. The scope of application is limited and it should not be used in high building construction. These are the known disadvantages of conventional vertical and horizontal surveying instruments.